1. Field of the Invention
The present invention relates to an ink jet recording head which records an image, such as characters, on a recording medium by ejecting ink droplets from a nozzle.
2. Description of Related Art
In general, in an ink jet recording head, a piezoelectric vibrating plate is affixed by adhesive to a part of a resilient plate comprising pressure generating chamber 6. The volume of the pressure generating chambers is changed by means of flexural displacements of the piezoelectric vibrating plate, thus ejecting ink droplets from a nozzle orifice. Such an ink jet recording head enables displacement of a wide area of the pressure generating chamber and hence is characterized by the stable ejection of ink droplets.
For example, as shown in FIG. 8, a conventional ink jet recording head includes an actuator unit which is formed by stacking up a resilient plate 113, a pressure generating chamber formation member 112, and a closure member 111, in this order from the top. The resilient plate 113 has a piezoelectric vibrating plate 117 placed thereon, thus constituting a vibration member. The pressure generating chamber formation member 112 forms a pressure generating chamber 115, one surface of which is sealed by the resilient plate 113. The closure member 111 seals the other surface of the pressure generating chamber 115 and has a supply communication path 122 for connecting the pressure generating chamber 115 to a supply hole 126 and a communication hole 120 for connecting the pressure generating chamber 115 to a nozzle orifice 121. A channel unit is formed by stacking up a supply hole formation substrate 124 having the supply hole 126 formed therein, a reservoir formation plate 123, and a nozzle plate 130, in this order from the top. The reservoir formation plate 123-has a reservoir 125, one surface of which is sealed by the supply hole formation substrate 124 and which is in communication with the pressure generating chamber 115 by way of the supply hole 126, and a communication hole 128 for connecting a nozzle orifice 121 to the pressure generating chamber 115. The nozzle plate 130 has the nozzle orifice 121 and seals the other surface of the reservoir formation plate 123. The ink jet recording head is formed by placing the foregoing actuator unit on the channel unit and bonding them together through use of an adhesive.
In such an ink jet recording head, if air bubbles remain in an ink flow channel, the air bubbles hinder ink supply or absorb pressure to eject ink, thus causing ink ejecting failures. Such air bubbles remain in the ink flow channel when the head is replenished with ink from an ink cartridge for the first time. In other cases, air bubbles enter the recording head from a connected portion between the head and the ink cartridge when the empty ink cartridge is replaced with a new ink cartridge. Alternatively, an ink meniscus in a nozzle is fractured by vibration, thus permitting entry of air bubbles into the recording head from the nozzle orifice. Thus a eliminator for these air bubbles is necessary in the ink jet recording apparatus. In general, there is provided a pump in the conventional recording apparatus. At the time of replacement of an ink cartridge or in the event of an ink ejecting failure, ink is forced out of the recording apparatus from the nozzle orifice by actuation of the pump, thereby producing an outflow for removing air bubbles.
However, the aforementioned conventional ink jet recording head suffers from inefficient discharge of air bubbles and a problem of air bubbles being likely to remain in corner portions of the ink flow channel as indicated by X and Y in FIG. 8 occurs. If the supply hole 126 is positioned close to the side wall of the supply communication path 122, air bubbles are urged to leave. However, increasing the positional accuracy of a bonding plane between the actuator unit and the channel unit is difficult. An adhesive squeezed along the bonding plane may fill the supply hole 126.